Lake Cachuma, Calif., has historically experienced severe hypolimnetic oxygen depletion during summer stratification. To alleviate this problem and improve the water quality of the reservoir, a diffused-air aeration system was installed in May 1981. A limnological study was conducted from April 1980 through November 1982. Results showed a weakening of the stratification, increased oxygen and temperature in the hypolimnion, increased green algae, and increases in the populations ofBosminaand Chironomids. Lake turnover in 1981 and 1982 occurred approximately one month earlier than in 1980. Water quality problems of manganese and hydrogen sulfide were effectively controlled.